This invention relates to apparatus for continuous vertical casting of metal strips and more particularly to apparatus of the kind comprising: a mould having top and bottom ends an open-ended mould cavity with a mould entrance opening at the top end and a strip exit opening at the bottom end, a tundish for holding molten metal, said tundish having a discharge opening in direct communication with the mould cavity to feed molten metal into the mould entrance opening past an interface between the tundish and the mould, a sealing device forming a seal at said tundish-mould interface to prevent molten metal from entering said interface, and a molten-metal feeding device for supplying molten metal to the tundish and maintaining a level of molten metal therein.
U.S. Pat. No. 3,797,555 A discloses continuous-casting apparatus of this kind. An important feature of such apparatus is that the mould has what is often referred to as a hot top, meaning that the level of the surface of the molten metal within the casting apparatus is substantially higher, namely within the tundish, than the level where the solidification of the molten metal against the chilled walls of the mould cavity is initiated.
In hot top continuous-casting apparatus there is thus a contiguous body of molten metal extending from some level within the tundish down to a level lower than the level within the mould cavity where solidification of the molten metal is initiated. Accordingly, there is no point within the mould cavity where the atmosphere can interfere with the solidification of the metal. Another advantage of the hot top casting technique is in the higher metallostatic pressure resulting from having the level of the molten metal in the tundish, rather than somewhere within the mould.
For the reliable operation of the casting apparatus and maintenance of a high quality of the cast, it is necessary to provide a reliable sealing at the tundish-mould interface, that is, at the point where the molten metal continuously fed into the mould flows through the discharge opening of the tundish and enters the mould cavity. Providing a reliable sealing is particularly difficult in casting apparatus where the mould is oscillated to facilitate the movement of the solidified metal through the mould cavity. It is also difficult to provide the large sealing surfaces, which are essential for a reliable sealing.